Aspects and embodiments of the invention most generally pertain to visual display apparatus and systems, image display methods, and applications. More particularly, aspects and embodiments are directed to 3D near-eye display systems for Virtual Reality (VR) and Augmented Reality (AR) systems, methods pertaining thereto, and applications thereof.
Conventional 3D near-eye displays for VR and/or AR applications use stereoscopic methods to realize 3D imaging effects by separately presenting two offset images to the left and right eyes of the viewer. Typically, one micro-display (e.g., OLED, LCOS, etc.) or portable display (such as a smartphone screen that is split into two sections, etc.) (hereinafter ‘display’) is used as an image source along with suitable optics to form a virtual image viewable by each eye. FIG. 1 shows an example of a Google Cardboard VR viewer wherein a smartphone screen is split into two sections to provide two offset images.
An image display is generally composed of an array of pixels (e.g., 1080×1200) as minimal display source elements. For VR applications, the display and optics are located in front of each eye to form the near-eye display. For AR applications, the display and optics are typically not directly located in front of each eye; rather, the virtual image is re-directed to the eye through a partial reflector (or diffractive element functioning as a partial reflector) so that the eye can also see the real world. FIGS. 2a and 2b, respectively, illustrate near-eye displays for one eye of a viewer for VR and AR applications.
During stereoscopic viewing the viewer is presented with two near-eye displays; one for the left eye and another for the right eye. Both eyes focus on each virtual screen, respectively, to see two offset images whose optical paths cross to form a 3D image. FIGS. 3a and 3b, respectively, illustrate differences between natural viewing and stereo viewing. In natural viewing, vergence and focal distance are equal. The viewer adjusts the vergence of the eyes to look at an object, and the eyes focus to sharpen the retinal image. Because of the tight correlation in natural viewing, vergence and accommodation are neurally coupled. Specifically, accommodative changes evoke changes in vergence (accommodative vergence), and vergence changes evoke changes in accommodation (vergence accommodation). In stereo viewing on a conventional stereo display, the focal distance is fixed at the distance from the eyes to the display screen, while vergence distance varies depending on the distance being simulated on the display. Thus a vergence-accommodation conflict is created when viewing a stereo display. To see the object clearly and without double vision the viewer must counteract the neural coupling between vergence and accommodation to accommodate to a different distance than the distance at which the eyes must converge. Visual fatigue and discomfort occur as the viewer attempts to adjust vergence and accommodation appropriately.
The literature describes a Zone of Comfort (ZoC) as a relationship between distance of vergence and distance to the screen (accommodation distance). Certain VR/AR applications such as, e.g., a computing platform suggest that the vergence distance of the 3D image should be less than 0.5 meter so that the viewer's hand can reach it easily. The ZoC suggests that the accommodation distance of the virtual screen should be less than one (1) meter for 0.5 meter comfort vergence distance. Currently available VR/AR devices either do not or cannot meet this requirement. The inventor has recognized the advantages and benefits provided by a solution to the vergence-accommodation problem, said solution being enabled by the invention claimed herein.